Ultra large scale integration (ULSI) of integrated circuit technology, which may be represented by 512M-bit and 1G-bit Dynamic Random Access Memories (DRAMs), may be achieved through high performance and high integration of semiconductor devices. Thus, as the minimum processing size required for the fabrication of devices becomes smaller, relatively small line widths (e.g., 60 to 70 nm) may be formed in the fabrication of next-generation devices.
Integration in integrated circuits has resulted in the reduction of the size of semiconductor devices and a need for multilevel interconnection. Highly integrated semiconductor devices may be fabricated by repeatedly and alternately depositing conductive and insulating materials over one another to form patterns. When the surface of each material layer is not planarized upon pattern formation, it may be difficult to form new pattern layers over the top. For example, in the case where new layers are continuously laminated on non-uniform surfaces between material layers, incident light may be reflected at different angles from refracted films, resulting in inaccurate photo resist patterns upon development. Thus, it may be necessary to planarize the surface of semiconductor materials in order to achieve effective lithography. Toward this end, chemical mechanical polishing (CMP) may be a desirable planarization technique. CMP of polycrystalline silicon may be particularly important because polycrystalline silicon materials are widely used to form contacts and lines in devices in semiconductor manufacturing processes.
CMP compositions generally include a slurry, which is typically an abrasive solution. In some processes, the slurry may be supplied to the space between the wafer and the surface of a polishing pad, so that the slurry may chemically react with the surface of the wafer while the polishing pad physically removes portions of the surface of the wafer.
Slurries used in semiconductor CMP processes may include, for example, deionized water, a metal oxide, a base or acid for pH adjustment, an additive for controlling the polishing rate and selectivity, and the like. Metal oxides may include silica, alumina, ceria, zirconia, titania, and the like, which are often produced by a fuming or sol-gel process. Amine-based additives may be helpful in achieving relatively high polishing rates towards polycrystalline silicon films, while at the same time, providing low polishing rates towards insulating layers.
Various methods of altering polishing slurries in order to increase the polishing rate in CMP processes have been attempted. For example, U.S. Pat. No. 4,169,337 discusses the addition of an echant, such as aminoethylethanolamine. U.S. Pat. Nos. 3,262,766 and 3,768,989 discuss the preparation of polishing compositions by co-precipitating small amounts of other particles, such as CeO2 particles during production of SiO2. Further, the addition of inorganic salts, such as Ce(OH)4, NH4SO4 and Fe(SO4), to a slurry is discussed in Mechanism of Glass Polishing Vol. 152, 1729, 1971. In addition, U.S. Pat. No. 4,169,337 discusses a slurry composed of silica/amine/organic salt/polyhydric alcohol; U.S. Pat. No. 4,169,337 discusses a slurry composed of silica/amine; U.S. Pat. No. 5,139,571 discusses a slurry composed of silica/quaternary ammonium salt; and U.S. Pat. No. 5,759,917 discusses a slurry composed ceria/carboxylic acid/silica; U.S. Pat. No. 5,938,505 discusses a slurry composed of tetramethyl ammonium salt/hydrogen peroxide.
Slurries used for polishing polycrystalline silicon films may have a polishing selectivity for polycrystalline silicon films relative to insulating oxide films that are used as stop layers. However, this polishing selectivity may result in dishing of the polycrystalline silicon films due to the chemical mechanical action. The occurrence of dishing may adversely affect subsequent photo processing, which may result in height differences upon the formation of polycrystalline silicon lines. As a result, the electrical properties and contact characteristics inside cells may be deteriorated. Thus, there is a need for slurry compositions that ameliorate or eliminate the problem of dishing and thus improve the within-wafer-non-uniformity.